THE SEED. 



45 



the milk- weed, or with more delicate fibres, as in cotton (Fig. 95). Some 

 seeds have an additional covering, more or less expanded in form, termed 

 an aril I US, or aril; of such character is the mace of nutmeg and the 

 scarlet pulp enclosing the seeds of the woody bitter-sweet (Cclastrus scan- 

 dens), so much used for winter decoration. 



All the expansions of the external seed-coat are evidently designed to 

 favor the distribution of the seeds. 



The scar left where the seed-stalk separates is termed the hilum ; the 

 minute orifice through which the pollen-tube entered, now closed up, is 

 termed the micropyle. 



The kernel is the essential part of the seed. In many seeds it is all 

 embryo — that is, a minute folded-up plantlet ; in others it comprises not 





Fig. 94. — Winged seed of the pine. 



Fig. 9.").— Cotton 



only the embryo, but a mass of nourishing matter in which this is im- 

 bedded, termed the albumen. 



The albumen is composed of starch, gluten, oily matters, etc., and is 

 designed to nourish the young plantlet during the early stages of its de- 

 velopment, before its roots have taken firm hold of the soil. It should be 

 borne in mind that this differs in every essential particular from animal 

 albumen. 



The embryo, or germ, is the embryo plantlet whose development we 

 have studied in the bean and Indian corn. It is distinguishable into three 

 parts, namely, (1) the radicle, called also and more properly the call lie I e, 

 or rudimentary stem, to one end of which are attached (2) the cotyle- 

 dons, or seed-leaves, between which is the rudimentary bud termed the 

 (3) plumule, while the other end becomes the descending axis. 



And here we leave this branch of our subject, having outlined, in a gen- 

 eral way, the history of flowering plants from their germination in the seed 

 to their reproduction in seed again. 



From this history that of flowerless or cryptogamous plants 

 differs in many essential particulars, but most of all in their earliest and 

 latest stages, in germination, and in reproduction. This subject cannot be 



